Current coal fired boilers employ burners located in the furnace wall (“wall burners”) to burn pulverized coal. These typically are used to make steam for generation of electricity.
Generally, pulverized coal is suspended in an air stream and blown into a boiler's furnace for burning. Air is introduced into the combustion chamber through registers along with the pulverized coal in a swirled fashion around a core of the pulverized coal stream. This provides more efficient burning and control over NO, emissions.
Combustion air is provided to the registers through an air conduit referred to as a ‘windbox’. The air passes from the windbox through the registers into the combustion chamber.
Some registers employ vanes that direct the incoming stream of air into a helical shape. The fuel stream passes longitudinally through the center of the burner and mixes with the swirling air from the register. The vanes may be moveable to adjust the swirl of air entering the register. The position of the vanes changes the ratio of axial airflow to tangential airflow.
These different flow patterns determine the shape and length of the flame produced and allow the proportion of the air's axial and tangential component to change the shape of the flame. The proper flame shape reduces flame quenching when it contacts the far boiler wall.
Therefore, it is important to be able to adjust the vanes to provide more efficient combustion.
In the prior art designs the linkage mechanism that controls the position of the vanes was located in the windbox. Typically, this is acceptable. However, when certain regenerative air heaters are used, exhaust gas impurities, such as flyash is transferred from the exiting flue gas into the windbox. Since the mechanism to rotate the vanes is also in the windbox, the accumulation of these impurities causes clogging and failure of the vane motion mechanism.
Prior art designs have the vanes on pivots between two parallel plates. The plate and vane closer to the combustion chamber experiences a higher temperature. The plate further from the combustion chamber experiences a lower temperature. The temperature differential causes differential expansion of the parts and structure. This variable expansion causes binding of the vanes between the plates. This binding prohibits the motion of the vanes, and leads to inefficient operation.
Since different vanes and different number of vanes may bind at different times, it introduces mechanical and reliability problems.
What further complicates the situation is that the mechanism that operates the motion of the vanes is typically located within the windbox. Its location is difficult to access for maintenance. It may require shutting down the boiler and may also require disassembly to access the windbox to adjust or repair the mechanism.
Currently, there is a need for an efficient burner for a furnace that is simple, inexpensive and more reliable than current designs.